UA 3873 then AA 884 at O'Hare
Fort Worth → Chicago → Miami
Timetable, Chicago time
17:55UA 3873 from Fort Worth at the gate
06:00AA 884 to Miami leaves the gate
12 h 05 apart on the timetable, overnight
AA 884 leaves 12 h 05 after UA 3873 arrives on the timetable: more than half a day, so not a connection we count.